1) Field
The general inventive concept relates to a surface acoustic wave (“SAW”) sensor device and, more particularly to a SAW sensor device that provides advantages which include, but are not limited to, substantially reduced sample loss, signal interference and noise.
2) Description of the Related Art
A surface acoustic wave sensor is a device that senses a target material, e.g., an analyte using a surface acoustic wave (“SAW.”) In general, a SAW is a mechanical wave generated from movement of particles due to thermal, mechanical or electrical power, for example, but not due to an electromagnetic wave. As a result, a majority of vibrational energy in the SAW is concentrated at a surface of a medium through which the SAW is transmitted.
Generally, the SAW sensor is disposed on a substrate made of a piezoelectric material, and includes a receptor attached thereto. The receptor specifically binds to a desired target material on a surface of the sensor. When a solution containing the target material flows to the SAW sensor, signals, such as wavelength, for example, are changed by mechanical, chemical and/or electrical reactions of the target material with the receptor. Accordingly, properties of the target material are quantified by monitoring changes in the signals.
The SAW sensor is particularly sensitive to changes pressure of a fluid and/or viscosity or density of a medium, as well as mass change on the surface. As a result, precise control of the fluid is very important to minimize noise, which is a signal change due to factors other than the mass change, for example.
In a typical SAW sensor, an oscillation technique of applying an output signal, emitted from an output inter-digital transducer (“IDT”), to an input IDT of the SAW sensor is used to generate a SAW in an electrode of the SAW sensor. In addition, a technique of generating a specific frequency outside the SAW sensor includes applying the specific frequency to the input IDT, and plotting an emitted output signal of the SAW sensor.
Although the oscillation technique provides increased sensitivity, this technique requires that an oscillator be installed in the SAW sensor. Moreover, the oscillator is generally in contact with and parallel to the SAW sensor.
In addition, large changes may occur in the SAW sensor, due to pressure gradients needed for fluid flow. Thus a plurality of the SAW sensors is typically driven in one chamber to reduce errors caused by the pressure gradients. Additionally, various tests may be rapidly conducted when one chamber includes a plurality of SAW sensors, because errors caused by a washing deviation are reduced and various target materials can be detected from one sample.
As a result, however, a plurality of SAW sensors are required and, since the oscillator is larger than the SAW sensors of the plurality of SAW sensors, a distance between the SAW sensors is limited due to the large size of the oscillator compared to the SAW sensors. Further, as the distance between the SAW sensors and the oscillator increases, losses of the sample increase and substantially interference of signals and/or noise is generated.